1. Field of the Invention
The invention relates to a driving assistance apparatus.
2. Description of Related Art
There is known a driving assistance apparatus that includes object detecting means (an ultrasonic sensor, a millimeter wave radar, or the like) for detecting an object around a host vehicle and that, for example, when a distance to an object is shorter than or equal to a predetermined distance, executes automatic braking control, or the like, irrespective of driver's operation to avoid a collision (see, for example, Japanese Patent Application Publication No. 2011-122607 (JP 2011-122607 A) and Japanese Patent Application Publication No. 2012-061932 (JP 2012-061932 A)).
Incidentally, the above-described object detecting means is generally provided outside a vehicle, so snow, or the like, may adhere to the object detecting means during traveling. If snow, or the like, adheres to the object detecting means, the object detecting means may detect the adhesion snow, or the like, that is not an original collision avoidance target, which may interfere with driving assistance.
Therefore, there has been suggested a technique for determining whether there is adhesion of snow (see, for example, Japanese Patent Application Publication No. 2011-215002 (JP 2011-215002 A)). In JP 2011-215002 A, when the length of a reverberation wave received by an ultrasonic sensor is larger than or equal to a threshold, it is determined that snow has adhered to a location around the ultrasonic sensor.
However, in JP 2011-215002 A, a determination as to whether there is adhesion of snow is carried out under an operating condition (another vehicle speed range) different from an operating condition (vehicle speed range) in which an object that is a collision avoidance target is detected. That is, it is not possible to determine whether it is adhesion matter, such as snow, or a hard obstacle at a close range on the basis of only the reverberation wave.